Flow testers for air are used in the mining industry to detect the flow of mine air and serve to detect weak air currents in rooms or industrial facilities. Such flow testers can, for example, be utilized for detecting the course of flow in ventilating and air conditioning installations, in laboratory exhausts and in drying equipment. These flow detectors can also be used in the mining industry for checking air in a mine at obscured regions or after flow obstructions have settled. Still another use of the flow testers is to detect leaks in pipelines and closures such as in furnaces.
Such flow testers are also advantageous when the distribution of vaporous toxic substances is to be estimated in working rooms. In this way, the measuring locations relevant for the air analysis can be selected.
The known flow tester for air comprises a flow testing tube and a small aspirator bulb mounted on the testing tube. The flow testing tube is first closed at both of its ends and for use, the testing tube is opened at both ends. The flow testing tube contains smoking sulphuric acid on a porous carrier and white aerosols form in the air flow which flows out of the flow testing tube when air passes therethrough. The white aerosols make the course of flow visible. The formation of aerosol is however greatly dependent on the moisture of the air and can substantially disappear when the air is very dry. Furthermore, the acidic characteristics of the aerosol are undesired in many instances.
U.S. Pat. No. 3,658,719 discloses a flow tester which includes a testing conduit made of elastic material which is connected to an aspirator bulb. The flow tester includes two components forming an aerosol which are accommodated in breakable ampules mounted one behind the other in the flow conduit. After the ampules are broken and when an air flow is generated, the one component is introduced into the flow path of the other component and the aerosol resulting from the mixture exits at the outlet of the flow tube. Such a configuration results in a relatively high flow resistance because of the placement of the two supply chambers one behind the other. This does not make possible a separate adaptation of the air quantities to the supply chamber through which a flow takes place.